This invention relates to composite plastic compositions useful in the preparation of simulated natural substances, such as stone-like and mineral-like materials. In particular the present invention involves the use of specific crosslinked polymers together with certain thermoplastic matrices to provide composite plastic compositions having a mineral-like appearance, especially an appearance similar to that of granite.
There currently exists a need for synthetic materials that mimic the appearance of mineral-like or ceramic-like materials, such as natural stone, and in particular granite, for use in the manufacture of flooring, tiles, counter tops, sinks, spas, sanitaryware, architectural articles and other ornamental materials. For example, acrylic “granite” sheet products useful in spas, sanitaryware and outdoor applications are currently prepared by cell or continuous casting processes where small granulates are suspended in monomer or monomer/polymer mixtures and then “cured,” such as is described in U.S. Pat. No. 5,304,592 and WO 97/14749. These thermoset materials can not be further fabricated by conventional thermoplastic processing methods (such as sheet extrusion and injection molding operations); furthermore, the thermoset processes currently require special handling steps or raw material limitations to uniformly suspend the granulates in the polymerizing matrix during the “cure” step. Reuse and recycling of waste and off-grade materials, such as trimmings, from prior art sheet materials is impractical due to the inherent intractability of the thermoset materials. Prior art “granite” sheet products prepared by casting methods generally have poor impact strength, for example brittleness, and are limited in their adaptability to various formulation or processing methods for producing final articles. In addition, the prior art materials often provide poor adhesion to substrate surfaces resulting in subsequent “delamination” of composite articles.
It is, therefore, desirable to be able to provide thermoplastic materials that may be fabricated by conventional thermoplastic equipment (such as extrusion or injection molding) for use in spas and outdoor architectural applications; there is a need for an economical and efficient method for reuse and recyling of waste materials that is not available with current thermoset casting processes.
The problem addressed by the present invention is to overcome the deficiencies of prior methods used to prepare mineral-like plastics by providing materials that are processable by less labor intensive methods, such as coextrusion or extrusion, while also improving the economics of the processing by allowing for reuse and recycling of waste materials.